The Effect of Secondary-Phase Fraction on the Deformation of Olivine plus Ferropericlase Aggregates: 1. Microstructural Evolution

To study the microstructural evolution of polymineralic rocks, we performed deformation experiments on two-phase aggregates of olivine (Ol) + ferropericlase (Per) with periclase fractions (f(Per)) between 0.1 and 0.8. Additionally, single-phase samples of both Ol and Per were deformed under the same experimental conditions to facilitate comparison of the microstructures in two-phase and single-phase materials. Each sample was deformed in torsion at T = 1523 K, P = 300 MPa at a constant strain rate up to a final shear strain of ? = 6 to 7. Microstructural developments, analyzed via electron backscatter diffraction (EBSD), indicate differences in both grain size and crystalline texture between single- and two-phase samples. During deformation, grain size approximately doubled in our single-phase samples of Ol and Per but remained unchanged or decreased in two-phase samples. Zener-pinning relationships fit to the mean grain sizes in each phase for samples with 0.1= f(Per)=0.5 and for those with 0.8= f(Per) =0.5 demonstrate that the grain size of the primary phase is controlled by phase-boundary pinning. Crystallographic preferred orientations, determined for both phases from EBSD data, are significantly weaker in the two-phase materials than in the single-phase materials.

Automated summary

To study the microstructural evolution of polymineralic rocks, deformation experiments were performed on two-phase aggregates of olivine (Ol) + ferropericlase (Per) with varying periclase fractions (f(Per)). Single-phase samples of Ol and Per were also deformed for comparison. Analysis of the microstructural developments using electron backscatter diffraction (EBSD) revealed differences in grain size and crystalline texture between single- and two-phase samples. Grain size increased in single-phase samples but remained unchanged or decreased in two-phase samples, indicating the influence of phase-boundary pinning. Crystallographic preferred orientations were stronger in single-phase materials compared to two-phase materials.